The present invention generally relates to charged particle beam exposure apparatuses and methods of controlling charged particle beam exposure apparatuses, and more particularly to a charged particle beam exposure apparatus which has the function of detecting a position detection mark of a continuously moving object which is to be subjected to an irradiation when carrying out an exposure process or the like, and to a method of controlling such a charged particle beam exposure apparatus.
Recently, exposure apparatuses employing an electron beam or an ion beam are used when exposing fine patterns in order to produce semiconductor integrated circuit devices such as large scale integrated circuits (LSIs) which have many functions and a high integration density.
When detecting the position detection mark on a semiconductor wafer which continuously moves, a reference is made to a position detection signal which is output from a stage moving/measuring device only for a first beam scan when reading the stage position. For this reason, when the stage moving speed is increased, it becomes difficult to positively deflect the electron beam onto the position detection mark on the semiconductor wafer.
Accordingly, there is a demand to realize a charged particle beam exposure apparatus which reads the stage position of the object for every unit beam scan instead of only reading the stage position for the first beam scan, so as to detect the position detection mark by taking into consideration the stage moving speed and to improve the speed of the exposure process or the like.
FIGS. 1 and 2 show essential parts of an example of a conventional electron beam exposure apparatus. The electron beam exposure apparatus shown in FIG. 1 includes an electron gun 1, a deflector 2, a secondary electron detector 3, a stage moving/measuring device 4 and an electron beam control unit 5. For example, a semiconductor wafer 6 is the object which is to be subjected to the irradiation. The electron beam exposure apparatus detects a position detection mark M on the semiconductor wafer 6 which moves at an extremely slow speed or is stationary, and thereafter exposes an LSI pattern and the like in an exposure region of the semiconductor wafer 6. For example, the position detection mark M is a mark groove.
FIG. 2 shows the internal construction of a main deflector unit 5A of the electron beam exposure apparatus. The main deflector unit 5A generally includes a counter 51, registers 52 and 53, a 2-input logical product circuit (hereinafter simply referred to as an AND circuit) 55 and a pattern generation circuit 54.
When detecting the position detection mark M of the semiconductor wafer 6, a scan control signal SE is set in the register 52 of the main deflector unit 5A from a digital signal processor (DSP, not shown) or the like in a higher level. On the other hand, a beam scan number N is set in the counter 51 as a scan number signal SC from a central processing unit (CPU, not shown) or the like in the higher level. As a result, a number of times (beam scan number) an electron beam 1A scans the position detection mark M is counted down in the counter 51, for example, and a main deflector control signal MD which indicates the end of each scan is output from the counter 51 based on this number. In addition, the AND circuit 55 obtains the logical product of the scan control signal SE and the scan number signal SC respectively set in the registers 52 and 53, and supplies the logical product to the pattern generation circuit 54. The pattern generation circuit 54 generates the scan control signal SE, a pattern generation busy signal PG and a pattern generation count signal PC based on this logical product. The sub deflection data (shot data) is generated during a time in which both the signals PG and PC have a high level.
Accordingly, the electron beam 1A scans the position detection mark M based on the predetermined number N which is set from the CPU or the like, and the secondary electron detector 3 detects a secondary electron image related to the position detection mark M.
Next, a description will be given of the operation of detecting the position detection mark M of the semiconductor wafer 6 which continuously moves, by referring to the flow chart of FIG. 3. First, a step P1 carries out a process of continuously moving the stage, and a step P2 carries out a process of reading the stage position.
Then, a step P3 carries out a process of calculating an error between a target position of the stage control and an actual stage position, and a step P4 carries out a process of determining a final deflection coordinate related to an electromagnetic deflection.
A step P5 carries out a process of correcting the deflection signals S2 and S3 of the electron beam 1A, and a step P6 carries out a process of deflecting the electron beam 1A onto the position detection mark M.
A step P7 decides whether or not the mark detection is ended. The step P7 is continued if the decision result in the step P7 is NO. On the other hand, if the decision result in the step P7 is YES, the process advances to a step P8, for example. The step P8 carries out a process of exposing an LSI pattern or the like in the exposure region of the semiconductor wafer 6.
Conventionally, when detecting the position detection mark M of the semiconductor wafer 6 which continuously moves and the process of reading the stage position is carried out in the step P2, a reference is made to the position detection signal S1 which is output from the stage moving/measuring device 4 only for the first beam scan.
For this reason, if the stage moving speed is increased, there is a problem in that it is difficult to positively deflect the electron beam 1A onto the position detection mark M of the semiconductor wafer 6 as shown in FIG. 4.
FIG. 4 is a timing chart for explaining the problems of the conventional apparatus described above. As shown in FIG. 4, when the stage moving speed is extremely slow or the stage is stationary, the process of detecting the position detection mark M can follow the moving stage within a range A in which the electron beam 1A can be deflected. However, if the stage moving speed is increased in order to speed up the exposure process, the stage may exceed the range A and fall within a range B in which no drawing by the electron beam 1A is possible. As a result, a control error is generated.
It may be regarded that the error is introduced in the deflection control of the electron beam 1A because the output timings of a main deflection blanking signal LB and a sub deflection blanking signal SB are determined by referring to the position detection signal S1 which is output from the stage moving/measuring device 4 only for the first beam scan by taking the stage position which is read the first time as the reference and no consideration is given as to the stage moving speed thereafter. Hence, even though the sub deflection blanking signal SB has a high level, it is difficult to positively deflect the electron beam 1A on the position detection mark M.
For example, if the number of going and returning shots of the electron beam 1A on the position detection mark M per unit scan is 400 and the exposure time per shot is 5 .mu.s, the time required per unit scan is 2 ms. In addition, the time required is 16 times and 32 ms if the scan is made 16 times.
Accordingly, if it is assumed that the stage is moving at 1 mm/s and the resolution of the stage position coordinate is 0.01 .mu.m, for example, a set pulse dependent on 0.1M scan control signals SE is repeated. In other words, the set pulse rises once in 10 ns.
For this reason, if the margin width of the sub deflection region is set to .+-.10 .mu.m, for example, the position detection operation is delayed and the range in which the drawing can be made on the stage is exceeded even when the stage moving speed is 1 mm/s, as is evident by comparing the time of 20 ms required for the stage to move a distance of 20 .mu.m and the time of 32 ms required for the electron beam 1A to scan the position detection mark M 16 times by the going and returning scan.